This invention relates to electric switches and more particularly to bistable, snap action electric switches. Still more particularly, the invention relates to electric switches of the aforementioned type commonly known as sump pump switches which control the starting and stopping of electric motors which operate pumps in response to the rise and fall of the level of water or other liquid.
A particular sump pump switch is shown in U.S. Pat. No. 4,196,325 issued Apr. 1, 1980 to S. A. Povilaitis and assigned by mesne assignments, to the assignee of this application. The disclosure of U.S. Pat. No. 4,196,325 is hereby incorporated by reference into this application. Disclosed in that patent is a two-pole overcenter snap action switch having a lever operator pivotally mounted in the housing and connected to a pivotally mounted U-shaped movable insulating contact carrier by a compression spring. The movable contacts for each pole are mounted on a common movable insulating contact carrier for simultaneous closing or opening with the stationary contacts of the two poles. To this end, it is important that the movable contacts be mounted to the movable insulating contact carrier for pivotal motion relative thereto in the general plane of the contact carrier to permit self-alignment of the movable contacts to the terminal members on which the movable contacts pivot. Previous methods for attaching the movable contacts to the contact carrier in a manner that would provide the self-alignment pivoting feature have proven costly and not entirely effective. In the aforementioned patent, the movable contacts are loosely attached to the U-shaped insulating movable contact carrier by rivets. When properly riveted, the movable contact is able to pivot about the rivet in the general plane of the contact carrier or the primary plane of the movable contact. However, it is difficult to maintain a consistent degree of looseness of a riveted connection from one contact to another. Riveting also represents an additional step in the manufacturing process.
A more recent commercial offering of the sump pump switch described above has provided clip-on movable contacts as shown in FIGS. 2 and 3 of the drawings. A U-shaped clip 42 is provided at one end of the movable contact 40 for mounting the contact to a movable insulating contact carrier 44. The insulating contact carrier is U-shaped and provided with a round hole 46 near the distal end of each of the outer legs. The contact 40 is provided with a semi-circular tab 48 which is sheared into the contact to mate with the round hole 46. Precise and consistent forming of the spring clip 42 is difficult to maintain. Moreover, semicircular tab 48 is preferably angularly offset to automatically snap into round hole 46 in the contact carrier 44 upon assembly. However, the relative short length of the tab compared to the length of the U-shaped clip renders the tab substantially more rigid than the clip. When inserting the contact carrier 44 into the spring clip 42, the tab 48 raises the contact carrier as it is inserted, causing the carrier 44 to rise up on the tab 48 and deflect the U-shaped clip 42 more widely open. Depending on the amount of deflection, the spring clip 42 can be unacceptably deformed. If the tab 48 is formed low enough not to cause deformation of the spring clip 42 upon assembly, it then provides insufficient engagement with the contact carrier 44 to retain the movable contact 40 on the carrier. This problem was resolved by an additional operation whereby the tab 48 was sheared into the contact 40, but not angularly offset upon fabrication of the movable contact and was subsequently deflected into the round hole 48 by an additional staking operation to increase the reliability of the engagement of the movable contact 40 to the contact carrier 44. Such additional manufacturing operations increase the cost of the switch.
The contact element 50 of the prior art movable contact shown in FIGS. 2 and 3 is riveted through a hole in the distal end of the movable contact 40. The height of the back portion of the rivet, i.e. the portion which is deformed over in the riveting process, also determined the amount of overtravel of contact carrier 44 after the movable contact element 50 engaged the respective stationary contact. The height dimension of the riveted portion of contact element 50 was difficult to maintain consistent so as to provide the desired overtravel and simultaneous contact closure or separation. Moreover, riveting the contact element represents yet another additional step and cost in the manufacturing process.